260 Prof. H. James-Clark on the Spongie ciliate 
nium, or Podophrya; and, as counter to what we see in these 
last, I would state that there are certain of the Vorticellians, 
closely related to Hpistylis, which have no stem whatever, and 
swim about as freely as Dysteria.” 
§ 16. PLEURONEMA, Duj. 
Pleuronema instabile*, Jas.-Clk. Pl. VII. figs. 75, 76. 
This infusorian bears such a strong resemblance to Hetero- 
mastix (§ 14) in some of its external features, that it seems as 
if it might more properly have succeeded the latter in the 
illustration of my subject; but mere resemblances do not al- 
ways indicate relationship: and in the case of Plewronema, in 
particular, this is most true; for it is decidedly a far more 
highly organized animalcule than Dysteria, as we shall see by 
what I shall now quote from an already published deserip- 
tion t :— 
“What I wish now to show in the Plewronema is the triple, 
or, I might say, even the quadruple diversity of the vibrating 
cilia, or, in other words, a quadruple specialization of one type 
of organs, by their manifold offices ranking their possessors 
above those of their class which attain to a less degree of 
complexity in this respect. ‘The most prominent of these cilia 
are those (fig. 75, cl!) which are arranged in longitudinal rows 
over nearly the whole extent of the body, and which most fre- 
quently are seen in a quiet state, projecting far out from the 
surface, like so many fine rigid bristles. In fact the motions 
of this animal are so lightning-like in rapidity, that I have 
never seen this form of cilia except when the body was in a 
quiet state; and therefore I judge that, as they do not move 
then, they are the principal organs of locomotion. ‘There is 
on the right side a group of much more heavily built cilia (c/), 
which project from the oblique furrow in which the mouth (m) 
is set. They are more particularly devoted to producing cur- 
rents inwhich the particles of food may be brought to the mouth. 
‘““'We see, also, projecting from the forward end of the 
oblique furrow, and near the anterior edge of the mouth (m), 
one of those proboscis-like lashes (fl) [a flagellum] which are 
so characteristic of the lower ciliate [flagellate] infusoria; but 
yet it would not seem to have the same office as in the latter, 
since it is usually held in this position, apparently as rigid as 
if it were a wire; and only now and then does it move, by a 
sudden jerk, and disappears in the oblique furrow—probably 
acting there in concert with the other cilia in the introduction 
of food into the mouth. The fourth and last kind of cilia of 
_ * See ‘Mind in Nature,’ wt supr. p. 148, fig. 90, + See note *, 
